1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the device.
2. Description of the Related Art
A widely popular capacitor of a ferroelectric memory employs the structure that a lead zirconate titanate (Pb(ZrxTi1-x)O3, to be called PZT hereinafter) thin film is sandwiched between a pair of electrodes. When a voltage is applied to this structure, the PZT is polarized. This polarization is not canceled if the power is turned off, and therefore the polarization can serve as a nonvolatile memory. As the polarization amount of the ferroelectric layer becomes larger, the signal amount is increased, and a device with a higher performance can be obtained. Although the PZT has a large polarization amount, the polarization amount is decreases as the cycle of write-in and read-out is repeated when ordinary Pt electrodes are used, (which is called fatigue characteristics).
The drawback of the decrease in the polarization amount of PZT can be avoided by using an electrode made of an electroconductive oxide, and conventionally, the use of, for example, strontium ruthenate (SrRuO3, to be called SRO hereinafter) has been proposed. A typical electrode made of SRO has a thickness of about 10 nm. In the case of the capacitor having a structure in which a PZT thin film is sandwiched between SRO electrodes, the decrease in the polarization amount (fatigue) does not develop even after 1015 times or more of rewrite. As compared to the case of the capacitor that employs the Pt electrodes, in which the fatigue develops after about 106 times of rewrite, the advantageous effect of the SRO electrodes is remarkable.
However, in the light of the current circumstances, the polarization amount obtained by the capacitor having a conventional structure in which a PZT thin film is sandwiched between SRO electrodes, is still not enough and there is an increasing demand for a further improvement in the polarization amount.